Turbine wheel and pelton turbine equipped with same

ABSTRACT

The invention concerns a Pelton turbine wheel comprising a rim ( 1 ) and several buckets ( 2 ) distributed at the rim periphery, characterised in that it comprises at least a ring-shaped flange ( 5, 6 ) integral with the rim and provided with housings ( 7 ) for receiving the buckets. The flange is capable of absorbing at least part of the efforts transmitted by the buckets ( 2 ) to the rim ( 1 ) and forms a peripheral strip ( 9 ) at external radial zones of the housings ( 7 ). The transmission of the efforts from the buckets ( 2 ) to the wheel rim ( 2 ) is carried out without generating too considerable a concentration zone of mechanical stresses.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a turbine wheel and to a Pelton-typeturbine equipped with such a wheel.

2. Brief Description of the Related Art

Pelton turbines are conventionally used for transforming the kineticenergy of a fluid, such as the water of a waterfall, into mechanicalenergy. Such transformation is effected by rotating the turbine wheelunder the effect of a tangential effort exerted, on buckets disposed onthe periphery of a wheel rim, by a jet of water emerging from one ormore injector nozzles distributed around the wheel.

The effort created on each bucket is transmitted to the wheel rimthrough an area of attachment of the bucket on the wheel rim. This areaof attachment, defined by the geometrical intersection of the bucketwith the rim, is subjected to considerable mechanical stresses. Ineffect, each bucket may be mechanically modelized as a beam fixed on oneside only, with the result that it undergoes a considerable bendingstrain due to the effort of the jet. In addition, high vibratorystresses are applied to the bucket and there is a danger of resonance ofthe bucket or the rim.

In known devices, particularly of EP-A-0 346 681 or of EP-A-0 522 336,attempts have been made to overcome these drawbacks by reinforcing thearea of attachment of the buckets on the wheel rim. This leads tostructures which are complicated and therefore expensive, and of reducedreliability. In addition, each bucket remains attached to the rim by oneside, with the result that the nature of the problems encountered is notfundamentally changed.

FR-A-704 875 teaches making the buckets of a turbine abut on one anotherby means of rings mounted on their periphery. The distribution of theefforts is not optimum and arms must be interposed between adjacentbuckets, being mounted with the greatest care, which results in anon-homogeneous distribution of the efforts.

SUMMARY OF THE INVENTION

It is a particular object of the present invention to overcome theseproblems by proposing a turbine wheel of Pelton type in which thebuckets are connected to the wheel rim so that the mechanical stressesare not concentrated in an area of attachment of the bucket to the rimand the dangers of resonance of the wheel are substantially reducedthanks to an optimalized distribution of efforts.

In that spirit, the invention relates to a wheel of the above type,which comprises at least one annular disk fast with the wheel rim andprovided with housings for receiving the buckets. This disk is adaptedto absorb at least part of the efforts transmitted by the buckets to therim and forms a peripheral band at the level of the outer radial areasof the housings.

Thanks to the invention, the disk which is on one piece and surroundsthe buckets, makes it possible to support them, near the rim, in anintermediate area and in an outer radial area, with the result that eachbucket is maintained efficiently in its inner, outer and central radialareas and that the effort to which it is subjected, due to the existenceof the jet of fluid driving the turbine, has for its effect to apply iton the disk. This effort is in that case not concentrated solely in onearea of attachment of the bucket to the wheel rim, but distributed overthe whole of the disk. In other words, the tangential effort created ona bucket is transmitted to the disk. The bucket and that part of thedisk supporting the bucket may be mechanically modelized as a beam ontwo bearings, and even a beam bearing on its length, the first bearingbeing towards the wheel rim, while the second bearing is constituted bythe peripheral band of the disk. Such a distribution of the effortsinduces a reduction of the stresses exerted on the mechanicalcomponents, which makes it possible to envisage pieces of lesserthickness.

Taking the foregoing into account, a turbine wheel according to theinvention may be made of metal, composite material or be a mixedstructure. For example, certain pieces, such as the wheel rim or thedisk, are made of metal, while other pieces, such as the buckets, aremade of composite synthetic material. A wheel rim or a disk made ofcomposite plastics material may also be associated with metal buckets.

In addition, the presence of the outer peripheral band of the disk,which creates a continuity of matter outside the wheel, makes itpossible substantially to reduce the vibratory stresses exerted on thebuckets. In effect, the peripheral band contributes to distributingthese stresses on the different buckets, with the result that theequivalent inherent mode of each bucket is no longer that of a beamfitted at one end only, as in the devices of of the prior art, but thatof a beam fitted on one side and bearing on or fitted on the other side.

Finally, it has been surprizingly found that the presence of the diskmakes it possible very substantially to improve the aerodynamicperformances of the wheel of the invention. In effect, the disk makes itpossible to limit the so-called “ventilator” effect of the wheel duringrotation, i.e. the recirculation of the air between the outside of thewheel and the spaces between two consecutive buckets, due to themovement of rotation. Such reduction of the transverse air movementswith respect to the buckets was able to be quantified, by laboratorytests, at about 20% of the braking force due to the ventilation of thewheel in the absence of disk. In this way, the invention also enablesthe yield of a Pelton turbine wheel to be substantially improved.

According to a first advantageous aspect of the invention, the wheelcomprises two disks disposed on either side of one or more injectornozzles of the turbine. This aspect of the invention makes it possibleto dispose the disks opposite each bowl or scoop of the buckets when thebuckets are double, as is conventionally the case in Pelton turbines. Inthat case, the disks may be provided to be substantially aligned on themedian axes of the scoops of the buckets.

According to another advantageous aspect of the invention, the disk ordisks is/are provided with spokes each adapted to substantially fill thespace separating two adjacent buckets of the wheel. Thanks to thisaspect of the invention, the spokes present a sufficient cross-sectionto absorb the mechanical stresses transmitted by the buckets. Moreover,the fact that they substantially fill the space separating two bucketsmakes it possible to optimalize the reduction of the “ventilator”effect.

According to a first embodiment of the invention, the disk or disksis/are in the form of a perforated ring, means for removably mountingthe or each disk on the wheel rim being provided near an inner edge ofthe or each disk.

According to a second embodiment of the invention, the disk or disksis/are formed in one piece with at least part of the wheel rim. Thanksto this aspect of the invention, transfer of the efforts of the disktowards the wheel rim is optimalized. In addition, assembly of theturbine wheel may be facilitated. In that case, the wheel rim may beprovided to be formed by two half-rims, each half-rim extending radiallytowards the outside by a disk.

According to another advantageous aspect of the invention, applicablewhatever the embodiment, the buckets are removably fixed on the disk ordisks and/or the wheel rim. This aspect of the invention guarantees agood dimensional stability of the wheel during use and an efficienttransfer of the efforts from the buckets towards the wheel rim. Inaddition, the operations of maintenance on the buckets or the disks arefacilitated.

According to another aspect, the bucket may be permanently fixed on thedisk or disks and/or the wheel rim.

The invention also relates to a Pelton-type turbine comprising a wheelas described hereinbefore. Such a turbine may be manufactured moreeconomically than the prior art ones since it is possible to optimalizethe dimensioning of the pieces by taking into account the fact that themechanical stresses are better distributed over the wheel. In addition,the yield of this turbine is improved by reduction of the ventilatoreffect.

The invention will be more readily understood and other advantagesthereof will appear more clearly from the following description of twoembodiments of a turbine wheel in accordance with its principle, givensolely by way of example and made with reference to the accompanyingdrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of a Pelton turbine wheel accordingto the invention.

FIG. 2 is a section along line II—II of FIG. 1.

FIG. 3 is a section along line III—III of FIG. 2, and

FIG. 4 is a view similar to FIG. 2 for a turbine wheel in accordancewith a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, the turbine wheel shown in FIG. 1comprises a wheel rim 1 and buckets 2, eighteen in number in the exampleshown, distributed on the periphery of the rim 1. Each bucket comprisestwo scoops 3 separated by a central edge 4 intended to be disposedopposite one or more water or steam injector nozzles (not shown). Therim 1 is provided to be mounted on a movement transfer shaft (likewisenot shown).

In order to render the drawing clearer, only one bucket has been shownin FIG. 1.

In accordance with the invention, two disks 5 and 6 in annular form aremounted on the rim 1 and contribute to maintaining the buckets 2 withrespect to this rim. The disks 5 and 6 are respectively provided withhousings 7 and 8 in which the scoops 3 of the buckets 2 are respectivelyinserted. The housings 7 and 8 may be machined or obtained by mouldingin the disks 5 and 6. Each of the disks 5 and 6 passes radially andoutwardly of the buckets 2, with the result that two continuous bands 9and 10 are respectively defined in the outer peripheral areas of thedisks 5 and 6. These continuous bands 9 and 10 connect spokes 11 and 12respectively belonging to disks 5 and 6. Each housing 7 of the disk 5 isdefined by two adjacent spokes 11 forming part of the disk 5 and by theband 9, while each housing 8 of disk 6 is defined by two adjacent spokes12 forming part of the disk 6 and by the band 10.

In this way, each bucket 2 is supported both by the wheel rim 1 and bythe two disks 5 and 6 which each form a one-piece annular ring aroundthe rim 1, with the result that the efforts of thrust F, visible in FIG.3 and transmitted to a bucket 2 by the jet of water or steam, aredistributed in efforts F′ in the spokes 11 or 12 of the disks 5 or 6from which they are transmitted to the rim 1. Part of these efforts mayalso transit via the area of attachment of the buckets on the rim as inthe known devices. Thanks to this distribution, the area of attachmentof the buckets 2 on the wheel rim 1 is not a critical mechanical stressarea.

Assembly of the buckets and the disks on the wheel rim 1 is more clearlyapparent in FIGS. 2 and 3. XX′ is the axis of the central edge 4 of abucket 2. The bucket 2 comprises two tabs 15 and 16 adapted to bedisposed on either side of an outer radial part 17 of the rim 1. Theelements 15 to 17 are respectively provided with a central bore 15 a, 16a or 17 a for receiving a locking screw 18. The disks 5 and 6 areprovided to be disposed on either side of the rim 1 and of tabs 15 and16 and comprise, near their respective inner edges 5 a and 6 a, bores 5b and 6 b provided to be aligned with bores 15 a, 16 a and 17 a, withthe result that the screw 18 successively traverses the disk 5, the tab15, the radial part 17, the tab 16 and the disk 6. In this way, disks 5and 6 and bucket 2 are removably mounted on the wheel rim 1.

The efforts F due to the water or steam jet transmitted to the differentbuckets 2 do not transit solely via the tabs 15 and 16 of each bucket 2,but are distributed over the periphery of the rim 1, thanks to the disks5 and 6 and, in particular, to bands 9 and 10.

In order to improve the rigidity of the assembly, and as is moreparticularly apparent in FIG. 3, area 17 of the rim 1 may be provided tobe made by removing material with respect to the nominal width of therim 1 which is conserved in the space 19 separating two continuous areas17.

It will be understood that the geometry of the spokes 11 and 12 isadapted to the outer shape of the buckets, with the result that thelatter are immobilized inside the housings 7 and 8 by cooperation ofshapes, this presenting the additional advantage that the spokes 11 and12 substantially fill the space separating two adjacent buckets of thewheel, with the result that the aerodynamic separation of the innervolume 20 defined between the two disks 5 and 6 with respect to theoutside of these disks is optimalized. In other words, the transversecirculation of air through the inner volume 20 is limited.

It will be noted that the disks 5 and 6 are substantially aligned on themedian axes AA′ and BB′ of the scoops 3 of the buckets 2. This inducesthe spokes II and 12 of the disks 5 and 6 to be spaced apart from thebottom of the scoops 3 by a distance d₁ and from the edges of the scoopsby a distance d₂, distances sufficient in order not to disturb the flowof water or steam towards the outside of the volume 20. The fact thatdistance d₂ is substantially smaller than distance d₁ corresponds to thefact that the spokes 11 and 12 substantially fill the space separatingtwo adjacent buckets.

As is more clearly apparent in FIG. 3, each bucket 2 is also renderedfast with the disk 6 thanks to a locking screw 21 housed in a bore 22 inthe disk 6 and adapted to engage in a rear boss 23 of the bucket 2. Anidentical construction is provided at the level of disk 5. The screw 21improves the immobilization of the bucket 2 with respect to the disk 5.

In the second embodiment shown in FIG. 4, elements similar to those ofthe embodiment of FIGS. 1 to 3 bear identical references increased by50. In this embodiment, the wheel rim 51 is formed by two half-rims 51 aand 51 b adapted to be assembled together, for example by means ofscrews 51 c.

The half-rim 51 a extends radially towards the outside by a one-piecering 55 forming an annular disk whose function is identical to that ofdisk 5 of the previous embodiment. The ring or disk 55 extends radiallyto the outside of a bucket 52 provided with two scoops 53 separated by acentral edge 54. Similarly, the half-rim 51 b extends by a ring orannular disk 56 adapted to support the buckets 52. The rings 55 and 56are provided with housings 57, 58 for receiving the buckets 52, whilecontinuous bands 59 and 60, respectively belonging to disks 55 and 56,define housings 57 and 58 in their outer radial part.

As elements 51 a and 55 on the one hand, 51 b and 56 on the other hand,are formed in one piece, transmission of the efforts between disks 55and 56 and the wheel rim 51 is optimal.

A Pelton turbine wheel according to this second embodiment is assembledby bringing the half-rims 51 a and 51 b towards each other, whilebuckets 52 are distributed radially in a position close to their finalposition, this making it possible to wedge a shank or tongue 52 a ofeach bucket 52 between the half-rims 51 a and 51 b, thus improving theanchoring of the buckets 52 with respect to the wheel rim 51. A screw 51c advantageously passes through the shank 52 a of each bucket 52.

According to a variant of the invention (not shown), the wheel rim 51and the disks 55 and 56 may be provided to be formed in one piece. Inother words, the half-rims 51 a and 51 b are in that case joined in onepiece, obtained by moulding and/or machining.

The effect of improvement of the ventilation of the turbine describedwith reference to the embodiment of FIGS. 1 to 3 is also obtained withthe device of the second embodiment.

Taking into account the relatively low level of stresses undergone bythe buckets and the rim of a turbine wheel according to the invention,it may be envisaged to make these pieces and the disks of materialswhich, up to now, were not envisaged for this type of device. Inparticular, the use of composite resin, possibly reinforced with fibers,may be envisaged, certain pieces still being able to be made of metal.

As the buckets can be manufactured independently of the wheel rim anddisks, they may be provided to be coated with an anti-abrasion oranti-erosion product before being assembled. In particular, thetechnical teaching of Applicants' Patent Application EP-A-0 543 753 maybe applied.

A turbine wheel according to the invention is assembled from a wheelrim, one or two disks, and from buckets or buckets bearingreinforcements. These different components may be assembled by the meansdescribed and shown in the Figures or by any other appropriate meanssuch as, in particular, cooperation of shapes, wedging, hooping,welding, soldering, adhesive bonding.

The invention has been represented with buckets removably mounted on thewheel rim and the disk. It is also possible to provide for these bucketsto be mounted permanently on the wheel rim and/or the disk, inparticular welded, soldered or bonded in position. Similarly, aone-piece wheel obtained by moulding may be produced, this wheelcomprising a rim, one or two disks and buckets.

What is claimed is:
 1. In a turbine wheel of the Pelton type, includinga wheel rim and a plurality of buckets spaced about a periphery of therim, the improvement comprising; at least one annular disk in the formof a continuous ring secured to the rim so as to extend radiallyoutwardly with respect to the rim, said at least one annular disk havinga plurality of spaced openings provided within an outer portion thereofspaced inwardly of an outer peripheral edge and radially outwardly ofthe rim for receiving the plurality of buckets, said at least oneannular disk extending radially outwardly relative to said plurality ofbuckets such that said plurality of buckets are positioned within saidspaced openings so that forces directed thereto are transmitted along afull length of each of said plurality of buckets to said at least oneannular disk such that said at least one annular disk is adapted toabsorb and transmit forces on said plurality of buckets to said rim, andsaid length being taken along a plane of said at least one annular disk;wherein said outer peripheral edge of said at least one annular diskforms a continuous annular portion of said at least one annular disk. 2.The turbine wheel according to claim 1, including two annular diskssecured in spaced relationship with one another to the rim forsupporting said plurality of buckets.
 3. The turbine wheel according toclaim 2, wherein each of said plurality of buckets includes two scoops,said two annular disks being substantially aligned on median axes (AA′,BB′) of said scoops.
 4. The turbine wheel according to claim 3, whereineach of said two annular disks include spokes which are integrally,connected at their outer ends and which spokes extend between twoadjacent of said plurality of buckets of the turbine wheel.
 5. Theturbine wheel according to claim 1, wherein said at least one annulardisk is in a form of a perforated ring, and means for removably mountingsaid at least one annular disk on the rim being provided in a vicinityof an inner edge of said at least one annular disk.
 6. The turbine wheelaccording to claim 1, wherein said at least one annular disk is formedin one piece with the rim.
 7. The turbine wheel according to claim 6,wherein the wheel rim is formed by two parts as half-rims adapted to beassembled together.
 8. The turbine wheel according to claim 1, whereinsaid plurality of buckets are removably mounted on said at least oneannular disk.
 9. The turbine wheel according to claim 1 wherein saidplurality of buckets are permanently mounted on said at least oneannular disk.
 10. A Pelton-type turbine comprising a turbine wheelincluding a wheel rim, and a plurality of buckets spaced about theperiphery of said rim at least one annular disk in the form of acontinuous ring secured to the rim and having a plurality of spacedopenings provided within an outer portion thereof spaced inwardly of anouter peripheral edge for receiving the plurality of buckets, said atleast one annular disk extending radially outwardly relative to saidplurality of buckets such that said plurality of buckets are positionedwithin said spaced openings so that forces directed thereto aretransmitted along a full length of said plurality of buckets to said atleast one annular disk and such that said at least one annular disk isadapted to absorb and transmit forces on said plurality of buckets tothe rim, and said length being taken along a plane of said at least oneannular disk; wherein said outer peripheral edge of said at least oneannular disk forms a continuous annular portion of said at least oneannular disk.